This is a Phase II Multicenter Trial of HN 66000, a proprietary pharmaceutical formulation of mutant diphtheria toxin and human transferrin that is being developed for malignant brain tumors. This is an open label, single treatment arm, stratified design (stratified by diagnosis). The primary clinical endpoint will be whether there was a 50% reduction (or greater) in tumor volume within twelve months after the second treatment with HN-66000.